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Old 12th Nov 2018, 5:19 pm   #1
Paul Mathew
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Default Mystery Octal

Not the only no-name brand in my collection, but is it possible to ID this one from the pics?
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Old 12th Nov 2018, 5:49 pm   #2
Neil Purling
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Default Re: Mystery Octal

That's a Mazda Octal valve. I can't tell what is the electrode structure or what is just a reflection in the glass.
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Old 12th Nov 2018, 6:24 pm   #3
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Default Re: Mystery Octal

Mazda octals have a wider space between the pins either side of the key but I don't recognise that as a Mazda valve. Looks a bit like an EL33.

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Old 12th Nov 2018, 6:38 pm   #4
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Default Re: Mystery Octal

NR77/EL35?

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Old 12th Nov 2018, 6:47 pm   #5
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Default Re: Mystery Octal

It does look like an output pentode or beam tetrode, but the heater voltage could be anything.
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Old 12th Nov 2018, 6:51 pm   #6
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Default Re: Mystery Octal

It does have something of the EL33/CL33 about it.
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Old 12th Nov 2018, 7:23 pm   #7
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Default Re: Mystery Octal

Might be able to narrow it down by finding out as to whether or not the anode is of mesh construction.

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Old 12th Nov 2018, 10:07 pm   #8
Hartley118
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Default Re: Mystery Octal

It looks like an EL37, that predecessor of the ubiquitous EL34.

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Old 12th Nov 2018, 11:15 pm   #9
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Default Re: Mystery Octal

According to the structure of the mica on top of the valve, it could be an EL35 such as this from the The National Valve Museum?
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Old 13th Nov 2018, 8:22 pm   #10
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Default Re: Mystery Octal

I also wonder whether it has a mesh anode.

If so it's probably an NR77 / EL35 / APW1295 like the one I have here, as Lawrence has also suggested.
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Old 13th Nov 2018, 8:32 pm   #11
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Default Re: Mystery Octal

Just another observation, the pics on the web appears to show that the EL35 and EL33 have a slight "waist" whereas the EL37 appears not to. The OP's photos seem to show a slight "waist"

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Old 14th Nov 2018, 2:15 am   #12
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Default Re: Mystery Octal

I have got some photos of the EL37 for comparison.
They have different micas and round flat anodes and certainly not mesh anodes.
The first photo is a pair with CV numbering in an amp that has now been restored and the second photo is a duff one showing that the anode indeed round.
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Old 14th Nov 2018, 1:48 pm   #13
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Default Re: Mystery Octal

Quote:
Originally Posted by Neil Purling View Post
That's a Mazda Octal valve. I can't tell what is the electrode structure or what is just a reflection in the glass.
Quote:
Originally Posted by Peter.N. View Post
Mazda octals have a wider space between the pins either side of the key but I don't recognise that as a Mazda valve.
It doesn't look like a MO to me either. Mazda Octals also have a larger central spigot - big enough to receive the pump-out tube and sealing pip - so that the whole electrode structure can sit lower down (more compact and lower stray inductances). This valve looks like no attempt has been made to take advantage of that. It may still be MO, of course, but somehow I doubt it.

If it IS a Mazda Octal, then that narrows choice down considerably of course! Maybe the OP can confirm.
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Old 15th Nov 2018, 3:05 pm   #14
Paul Mathew
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Default Re: Mystery Octal

Unfortunately there is not a single marking to hint at manufacturer or type. Looking at a close-up here: http://www.r-type.org/exhib/aaa1624.htm
it looks like an EL35. The main body of mine is blacked out so it's not possible to see the mesh anode mentioned. It has a curious little mesh near the base facing downward on a single arm. FWIW the reading between pins 2 and 7 is 2 Ohm. I'll try and post clearer pics.
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Old 15th Nov 2018, 6:51 pm   #15
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Default Re: Mystery Octal

Quote:
Originally Posted by Paul Mathew View Post
It has a curious little mesh near the base facing downward on a single arm. FWIW the reading between pins 2 and 7 is 2 Ohm. I'll try and post clearer pics.
Pins 2& 7 are of course the heater connections - fairly standard in Octal valves.

I could be wrong, but the 'curious little metal thing' sound like the 'getter', which is used during the latter part of the production of a valve to get rid of impurities inside the valve after the vacuum has been created. On many valves you'll see a mirror-like deposit on the inside of the glass close to the getter, deposited when the getter is 'flashed'. Sometimes the getter is a little ring like a halo at the top of the inside of the valve, which - when flashed - creates a mirror like deposit at the dome of the valve.

When the valve has been flashed, the getter's work has been done, but it doesn't stop audiophools from thinking that one shape of getter is better than another and can improves 'tonal qualities' giving the valve an 'airy presence'. Using the term 'air' in the context of valves usually means the valve has gone down the gurgler.

From Wiki:

Quote:

8-<

Flashed getter – The getter material is held inactive in a reservoir during assembly, then heated and evaporated after initial evacuation, usually by induction heating. The vaporized getter, usually a volatile metal, instantly reacts with any residual gas, then condenses on the cool walls of the tube in a thin coating, the getter spot or getter mirror, which continues to absorb gas. This is the most common type, used in low power vacuum tubes.

8-<

https://en.wikipedia.org/wiki/Getter

About 4 mins 15 secs into this video about hand-made high-end audio valves, you'll see a getter being inductively flashed:

https://www.youtube.com/watch?v=DOR6Pn-tGPo

Hope that's of interest.
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Old 15th Nov 2018, 8:30 pm   #16
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Default Re: Mystery Octal

Quote:
Originally Posted by David G4EBT View Post
When the valve has been flashed, the getter's work has been done
Maybe for the support ring but not for the getter material.

It's possible for a getter support to affect the performance of a valve, eg: microphony due to it being insufficiently supported.

Lawrence.
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Old 19th Nov 2018, 8:40 am   #17
Paul Mathew
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Default Re: Mystery Octal

All very interesting! Glad I only have to plug valves in and not make them!
I have noticed the halo ring near the top in many wire pin valves, and the silver lining in close proximity. That explains the silver lining near the bottom of this valve close to the little grid as seen in the pic attached. As an aside, I recently used a dud valve and sprayed the top cap grey to give it an appearance of a working valve with a led light for effect on a Quad amp. Small things...........
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Old 19th Nov 2018, 9:34 am   #18
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Default Re: Mystery Octal

Have you tried the trick of breathing on the glass so that your breath condenses there. This can give a momentary view of faint lettering.

Try it on the top as well as the sides.

Peter
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Old 19th Nov 2018, 9:47 am   #19
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Default Re: Mystery Octal

Quote:
Originally Posted by peter_scott View Post
Have you tried the trick of breathing on the glass....
Another trick that sometimes works is viewing the valve in the light of an LED torch.
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Old 19th Nov 2018, 10:13 am   #20
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Default Re: Mystery Octal

I have a number of these BRIMAR 6L6GA valves. They look very similar to the one illustrated. They may have an AMERTY connection dating from WW2.
John.
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